There is known issue with some archiver programs like winrar or standard windows integrated archiver.

We always testing with http://www.7-zip.org so please use it for extract and everything should be fine

Or via cpanel/plesk file manager, complete process is described here:

For cpanel: http://iwinter.com.hr/support/?p=4833

For plesk: http://iwinter.com.hr/support/?p=6991